Some conventional electronic lead attachment apparatus employ a laser beam to deliver a high energy pulse to a lead which is to be attached. The lead is thereby bonded to a metallic terminal, such as a bonding pad, by the melting and subsequent freezing of eutectic solder material. One problem associated with such a soldering operation, wherein where either the solder is heated directly or a lead is heated to melt the solder, is that only a relatively small portion of the laser energy is utilized for heating while a significant portion of the energy is reflected or scattered. In addition to this inefficiency resulting from the laser reflection the reflected laser radiation may pose a safety hazard to personnel in the immediate vicinity. Wavelength optimization of the laser beam to maximize absorption has been found to reduce but not eliminate the energy losses.
Another problem which is encountered with conventional laser soldering methodology is related to the sequential nature of the process and the significant amount of time required to solder all of the leads of an electronic device. In that modern electronic components may have one hundred or more leads, and a typical assemblage of such components may comprise some arbitrarily large number of components, a significant amount of time and cost is required to attach all of the leads to bonding pads. Related to this problem is the necessary repositioning of either the laser beam or the leads between soldering operations. That is, each lead is individually exposed to the laser beam by either an x-y positioning of the component or by optically scanning the beam over stationary leads. In both cases, the maximum rate of lead attachment has been found to be only approximately 10 leads per second.
In view of the above mentioned and other problems it can be appreciated that the use of laser soldering for component attachment may be less than an optimum technique in spite of the high process reliability and high joint quality produced by this technique.
Other soldering apparatus such as electrically heated tools may deliver too much heat to a localized area of a component or a printed circuit board, resulting in failure of the component or physical damage to the printed circuit board.
It is thus one object of the invention to provide a laser soldering apparatus and method which utilizes a significantly greater portion of the laser beam power than conventional techniques while also eliminating the possibility that laser radiation will be reflected or scattered into the environment.
It is another object of the invention to provide a laser soldering apparatus and method which is capable of simultaneously soldering a plurality of leads to associated bonding pads, thereby significantly increasing the speed and reducing the costs associated with conventional laser soldering techniques.